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# Chapter 9 test make-up by G2iv1V

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1. An opinion poll asks a random sample of adults whether they favor banning
ownership of handguns by private citizens. A commentator believes that more than
half of all adults favor such a ban. The null and alternate hypotheses you would use
to test this claim are

2. Bags of a certain brand of tortilla chips claim to have a net weight of 14 ounces. Net
weights actually vary slightly from bag to bag and are Normally distributed with a
mean  . A representative of a consumer advocate group wishes to see if there is any
evidence that the mean net weight is less than advertised and so intends to test the
hypotheses

H o :   14; H a :   14 To do this, he selects 16 bags of this brand at random and
determines the net weight of each. He finds that the sample mean to be x  13.82 and
the sample standard deviation to be s 0.24 .
We conclude that we would

3. A type I error in the previous question would mean

4. You are thinking of using a t procedure to test hypotheses about the mean of a
population using a significance level of 0.05. You suspect that the distribution of the
population is not Normal and may be moderately skewed. Which of the following
statements is correct?

5. After once again losing a football game to the archrival, a college’s alumni
association conducted a survey to see if alumni were in favor of firing the coach. An
SRS of 100 alumni from the population of all living alumni was taken. 64 of the
alumni in the sample were in favor of firing the coach. Suppose you wish to see if a
majority of living alumni are in favor of firing the coach. The appropriate test
statistic is

6. We prefer the t procedures to the z procedures for inference about a population mean
because
7. Looking online (for example, at espn.go.com) you find the salaries of all 22 players
for the Chicago Cubs as of opening day of the 2005 baseball season. The club total
was \$87 million, eighth in the major leagues. Which inference procedure would you
use to estimate the average salary of the Cubs players?

8. You read in the report of a psychology experiment that “separate analyses for our two
groups of 12 participants revealed no overall placebo effect for our student group
(mean =0.08, SD = 0.37, t(11) = 0.49) and a significant effect for our non-student
group (mean = 0.35, SD = 0.37, t(11) = 0.38, p < 0.01).” Are the two values given for
the t test statistic correct? (The null hypothesis is that the mean effect is zero.)

9. A sociologist is studying the effect of having children within the first two years of
marriage on the divorce rate. Using hospital birth records, she selects a random
sample of 200 couples who had a child within the first two years of marriage.
Following up on these couples, she finds that 80 couples are divorced within 5 years.
To determine if having children within the first two years of marriage increases the
divorce rate we should test

10. In order to study the amounts owed to a particular city, a city clerk takes a random
sample of 16 files from a cabinet containing a larger number of delinquent accounts
and finds the average amount x owed to the city to be \$230 with a sample standard
deviation of \$36. It has been claimed that the true mean amount owed on accounts
of this type is greater than \$250. If it is appropriate to assume that the amount owed
is a Normally distributed random variable, the value of the test statistic appropriate
for testing the claim is

11. What is the value of t * , the critical value of the t distribution with 8 degrees of
freedom, which satisfies the condition that the probability is 0.10 of being larger
than t * ?

12. Which of the following 95% confidence intervals would lead us to reject
H o : p  0.30 in favor of H a : p  0.30 at the 5% significance level?

An SRS of 100 postal employees found that the average time these employees had
worked at the postal service was x =7 years with a standard deviation of s = 2 years. Are
these data evidence that the mean  for the population of postal employees has changed
from the value of 7.5 years 20 years ago? To determine this, we test the hypotheses
H o :   7.5; H a :   7.5 with a one-sample t test.

13. What conclusion should you draw from a test at the 5% significance level?
14. Suppose we are not sure if the population distribution is Normal. In which of the
following circumstances would use of the t procedure yield misleading results?

15. You have data on rainwater collected at 6 locations in the Adirondack Mountains of
New York State. One measurement is the acidity of the water, measured by pH on a
scale of 0 to 14 (the pH of distilled water is 7.0). Which inference procedure would
you use to estimate the average acidity of rainwater in the Adirondacks?

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